a) Field of the Invention
The present invention relates to a cryogenic cooling system for superconductive electric machines, and more particularly, relates to a cryogenic cooling system for superconductive electric machines suitably used for cooling equipments that require a large refrigeration load such as a superconductive generator, and effective for improvement in efficiency and miniaturization of an apparatus.
b) Description of the Related Art
A superconductive generator requires cooldown for lowering the temperature of a rotor to the operating temperature thereof, and cryogenic cooling for maintaining the rotor in a low temperature for the normal operation.
However, with regard to cooling of the superconductive generator, no attempt has heretofore been made worldwide to put it to practical use. As a conception, there can be considered to circulate cryogenic liquid helium from outside to effect cooling. This is because since the superconductive generator has a rotor, it is difficult to soak it directly in the liquid helium.
However, with the method of circulating the liquid helium from outside to cool the superconductive generator, the liquid helium is warmed up and gasified, at the time of cooling the superconductive generator. Therefore, it is necessary to throw away the warmed and gasified helium to prevent becoming high pressure state, and to supplement the liquid helium at all times, causing a problem in that much labor and cost are required.
It is an object of the present invention to efficiently attain two objectives: cooldown of an object to be cooled up to the operating temperature; and maintaining a low temperature for the normal operation.
It is another object of the present invention to increase the redundancy of the system to thereby improve the reliability.
In order to achieve the above-described objects, the present invention provides a cryogenic cooling system for superconductive electric machines comprising a refrigerant transfer system and circulation means for internal circulation within the cryogenic area.
The superconductive electric machines ma y be a generator, a motor, a coil, a bulk or the like.
The cryogenic cooling system for the superconductive electric machines may comprise a cryocooler for cooling a system, a forced flow refrigerant transfer system for cooling the superconductive electric machines, and a cold box for housing the cryocooler and the transfer system.
The inside of the cold box may be vacuum.
There may be provided, outside of the cold box, at least one compressor for supplying high pressure refrigerant gas to the cryocooler, and a circulation pump for circulating the refrigerant gas to the forced flow transfer system.
The cold box may comprise: at least one closed cycle cryogenic refrigerator; a heat exchanger; at least one rejection heat exchanger provided on the cryogenic refrigerator; and piping for forcedly circulating the refrigerant gas.
Also, the redundancy of the system is increased to improve the reliability, by providing a plurality of cryogenic refrigerators.
Moreover, a sleeve for removing the cryogenic refrigerator from the cold box is provided to thereby make the maintenance easy.
An ejector for directly returning a part of the refrigerant gas returning from the superconductive electric machine to the rejection heat exchanger is also provided, thereby enabling improvement in efficiency.
Furthermore, a radiation shield plate for insulating the cryogenic area from the radiation from the normal temperature area is provided to thereby improve the cooling performance.
As described above, by directly circulating a part of the refrigerant in the low-temperature state, the amount of refrigerant passing through the heat exchanger on the normal temperature side is reduced, thereby enabling improvement in the overall thermal efficiency. Moreover, the apparatus can be made small by reducing the size of the heat exchanger and making the circulation pump small.